@MISC\{IMM1993-02772,
    author       = "N. K. Poulsen and J. Holst",
    title        = "Kalman Filtering with Unknown Variance Level",
    year         = "1993",
    publisher    = "",
    address      = "",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/2772-full.html"
}